Considerable effort has been made to develop carbon containing coatings having particular desirable properties, i.e., synthetic diamond coatings, sometimes characterized as glassy diamond coatings, amorphous diamond coatings, and disordered diamond coatings. These coatings are characterized by unique photoluminescent, electroluminescent, optical, corrosion resisting, and ultimate properties. However, various problems are associated with the attainment of such "diamond like" properties. These problems are believed to be associated with microvoids, dangling bonds, a high number of carbon-hydrogen bonds, and carbon-carbon double bonding.
Two distinctly different methods of depositing carbon coatings in an attempt to avoid these problems and to attain properties associated with tetrahedral coordination are reported in the literature. In one method, described, for example, by Aisenberg and Chabot in Journal of Applied Physics, Vol. 42 (1971) at p. 2953, diamond-like films are deposited using an ion beam of carbon produced in an argon plasma and then introduced into a low vacuum vessel. While the reported hardness, electrical resistivity and chemical inertness of the films and coatings produced thereby are reported to be satisfactory, the production rate of the method was reported to be low.
Subsequently, Whitmell and Williamson demonstrated a method of obtaining hard carbon containing films by cracking a gaseous, linear hydrocarbon in a direct current glow discharge. In the Whitmell and Williamson process described in D. S. Whitmell and R. Williamson Thin Film Solids, Vol. 35 (1976) at p. 255, the substrate is placed on a negatively biased target electrode and the direct current plasma exposes the substrate to a hydrocarbon gas decomposing plasma.
Subsequently, Holland and Ojha developed a process described in Thin Film Solids, Vol. 38 (1976) at p. L-17, Thin Film Solids, Vol. 40 (1977) at p. L-31, and Thin Film Solids, Vol. 48 (1978) at p. L-21. In the process of Holland and Ojha, hard, carbon containing films are obtained by cracking gaseous linear hydrocarbons in a radio frequency glow discharge. In the process of Holland and Ojha, the substrate is placed on a negatively biased target electrode and the radio frequency excited plasma exposes the substrate to positive ions and to electrons alternately. This prevents any net charge accumulation on the insulating deposits.
The reported hardness, electrical resistivity, optical absorbtion, chemical inertness, and index of optical refraction of the films produced by the method of Holland and Ojha indicated a disordered structure characterized by the substantial absence of carbon hydrogen bonds and the postulated presence of a small number of tetrahedral, four-fold, carbon-carbon coordination in an otherwise graphitic structure.